Device for heater movement in crucible-free zone melting a crystalline rod

ABSTRACT

Device for crucible-free zone melting a crystalline rod includes a zone-melting chamber having a sidewall formed with a substantially vertical slot, heating means extending through said slot into said chamber and energizable for forming a melting zone in a substantially vertically supported crystalline rod mounted in said chamber, slide means located adjacent said sidewall and carrying said heating means, said slide means and said heating means being slidable together relative to the rod in the direction of the rod axis whereby the melting zone is passed through the rod, and an elastically deformable sealing strip mounted between said slide means and said sidewall of said zone melting chamber and completely surrounding said slot whereby said slot is gastightly sealed, said sealing strip being secured against displacement.

United States Patent [72] Inventor Wolfgang Keller Pretzfeld, Germany [21] Appl. No. 669,979 [22] Filed Sept. 22, 1967 [45] Patented Dec. 28, 1971 [73] Assignee Siemens Aktiengesellschaft Berlin and Munich, Germany [32] Priority Sept. 24, 1966 [33] Germany [31] S 106086 [54] DEVICE FOR HEATER MOVEMENT IN CRUClBLE-FREE ZONE MELTING A CRYSTALLINE ROD 3 Claims, 5 Drawing Figs.

[52] US. Cl 23/273 SP, 23/301 SP 1 1 [56] References Cited UNITED STATES PATENTS 2,990,257 6/1961 Heneage et a1.. 23/273 3,119,778 l/l964 Hamilton 23/273 X t PliE-HEATER 10 HEATER i R AFTER- 7 HEMER 9 Primary Examiner- Norman Yudkoff Assistant Examiner-R. T. Foster Attorneys-Curt M. Avery, Arthur E. Wilfond, Herbert L.

Lerner and Daniel J. Tick ABSTRACT: Device for crucible-free zone melting a crystalline rod includes a zone-melting chamber having a sidewall formed with a substantially vertical slot, heating means extending through said slot into said chamber and encrgizable for forming a melting zone in a substantially vertically supported crystalline rod mounted in said chamber, slide means located adjacent said sidewall and carrying said heating means, said slide means and said heating means being slidable together relative to the rod in the direction of the rod axis whereby the melting zone is passed through the rod, and an elastically deformable sealing strip mounted between said slide means and said sidewall of said zone melting chamber and completely surrounding said slot whereby said slot is gastightly sealed, said sealing strip being secured against displacement.

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SHEET 1 BF 3 ALING STRIP L-l-el DEVICE FOR HEATER MOVEMENT IN CRUCIBLE-FREE ZONE MELTING A CRYSTALLINE ROD My invention relates to a device for crucible-free zone melting a crystalline rod, especially a semiconductor rod.

In U.S. Pat. No. 3,39l ,235 of R. Emeis, issued July 2, l968 and assigned to the assignee of the instant application, there is disclosed a device for crucible-free zone melting a vertical, end-supported crystalline rod, of semiconductor material especially. The device includes a heater displaceable relative to the crystalline rod in the direction of the rod axis and a holder for the heater carried in a slide which gastigl'itly closes a vertical slot formed in a sidewall of a zone melting chamber. Such a device presents the advantage that the distance between the source of energy and the terminals of the electrical heater can be kept very small so that, particularly when using an inductive heating device, the inductance of the supply leads of the heating circuit is small, resulting in less losses for the heating device. Moreover, the device of the aforementioned copending application is marked by a highmechanical stability for the heating device.

It is an object of my invention to provide a device of the foregoing type retaining the advantages thereof but also improving the cooperation of the slide and the zone-melting chamber. More particularly it is an object of my invention to provide a device which will improve the sealing and will minimize the friction between the parts sliding on one another. Moreover, it is a further object to provide a device that will not only be applicable for performing the zone-melting operation in vacuo but also under protective gas, and preferably at superpressure.

With the foregoing and other objects in view, I provide in accordance with my invention an elastically deformable sealing strip mounted between the slide and the sidewall of the zone-melting chamber and completely surrounding the substantially vertical slot, the sealing strip being secured against displacement.

The annular surface of the sealing strip closed upon itself is the only friction surface. Thereby, especially for very large displacement distances of, for example, 1 meter and more, the friction between the zone-melting chamber and the displaceable slide is considerably reduced when compared with that of the device disclosed in the aforementioned copending application.

In accordance with further features of my invention, the sealing strip is formed of one or more sealing lips curved toward one another, the position of which is determined by support members. The sealing lips are pressed by a pressurized medium against the sliding surface of the slide. Leak losses can thereby even then be prevented with great assurance, if a liquid such as oil, for example, is used as the sealing medium. Moreover, the sealing pressure between the sealing element and slide is controllable in a simple manner by varying the pressure of the pressure medium. In accordance with additional advantageous features of my invention, easily moving guide elements are mounted between the sidewall of the zonemelting chamber and the slide. Therewith, an excellent guidance and an especially easy and exceptionally smooth movement of the slide are afforded.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in device for crucible-free zone-melting a crystalline rod, especially a semiconductor rod, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a vertical sectional view of a zone-melting device constructed in accordance with my invention;

FIG. 2 is a view of FIG. I as seen from the thereof with the slide removed;

FIG. 3 is a vertical sectional view partly broken away of another embodiment of the zone-melting device of FIG. 1;

FIG. 4 is a view of FIG. 3 as seen from the right-hand side thereof with the slide partly broken away; and

FIG. 5 is a cross-sectional view of a horizontal wall of a zone-melting chamber further embodying the invention.

Referring now to the drawings, and first particularly to FIGS. 1 and 2 thereof, there is shown a zone-melting chamber 1. A nonillustrated evacuating device can be connected to the zone-melting chamber 1; however, the chamber 1 can also be filled with a protective gas such as argon for example, at superpressure if necessary. Drive shafts 2 and 3 for end holders 4 and 5 of a crystalline rod 6, such as of semiconductor material, are vacuumtightly and gastightly inserted in the zone-melting chamber 1 in a known manner. A melting zone 7 is produced by a heating device 8 and, if desired, the heating device 8 can be preceded by a preheating device 10 or followed by an afterheating device 9 or both preceded and followed by the respective-heating devices 10 and 9. Holders ll, 12 and 13 for the heating devices 8, 9 and 10, respectively, are gastightly and vacuumtightly clamped in a displaceable slide 14 and extend laterally into the zone-melting chamber 1 through a vertical slot 15 formed in a sidewall 16 of the zone-melting chamber 1. A guide plate 17 is secured on the sidewall 16 of the zonemelting chamber 1 and is provided with an opening 17a corresponding to the vertical slot 15. Instead of the guide plate 17, the sidewall 16 of the zone-melting chamber 1 can be increased in length in the vertical direction beyond the horizontal melting chamber walls 18 and I9 and can thereby serve directly as guide for the displaceable slide 14. An elastically deformable sealing strip 20 is mounted between the slide 14 and either the guide plate 17 or the lengthened sidewall 16 of the zone-melting chamber 1 and completely surrounds the vertical slot-15 in the sidewall 16 of the zone-melting chamber 1. The sealing strip 20 can advantageously be formed of two oppositely curved sealing lips 21, 22, secured in position by support members 23. The support members 23 advantageously completely surround the face of the sealing lips 21, 22 and are secured either to the guide plate 17 or to the slide 14. The intermediate space between the sealing lips 21, 22 is filled with a medium 24 maintained under pressure. The medium 24 is preferably a liquid such as oil, for example. The sealing lips 21, 22 are thereby pressed against both the guide plate 17 as well as the displaceable slide 14. By varying the pressure of the medium 24, the sealing pressure of the sealing right-hand side lips 21, 22 is greatly varied. For secure guidance of the slide I 14 on the guide plate 17 and for reducing the frictional resistance, easily moving guide elements, for example ball-bearing slides 25, are mounted between the guide plate 17 and the slide 14 and are guidable within rails 26 and 27 in the guide plate 17 and in the slide 14. A pressure plate 28, which can have the form of a pressure rail, if necessary, ensures guidance of the slide 14 on the guide plate 17 free of any play. A ballbearing slide 29, similar in construction to the ball-bearing slide 25, is mounted between the pressure plate 28 and the slide 14. Instead of the ball-bearing slides 25, 29, other known easily movable bearings, for example roller bearings mounted perpendicularly to the displacement direction of the slide 14 or also ball guides can be used.

A further especially advantageous embodiment of the invention is shown in FIGS. 3 and 4. Guide rollers 30 mounted on fixed shafts serve as guide elements for the slide 14 at the upper and lower ends of the sidewall 16 of the zone-melting chamber 1. If necessary, additional guide rollers can be mounted laterally of the vertical slot 15 especially for vacuum zone-melting installations. Guide rails 32 located laterally on the slide 14 pass between the guide rollers 30 as well as the corresponding counterpressure rollers 31. The sealing strip 20 is advantageously embedded in the polished sidewall 16. The length of the slide 14 and of the guide rail 32 is about double the length of the vertical slot 15. With such a construction, an

additional guide plate is no longer required. It is furthermore advantageous that the guide rollers and the counterpressure or reaction rollers 30, 31 are fixedly mounted'and the spacing therebetween is thereby constant.

it is apparent that the sealing strips 20 can also be modified extensively. Instead of the illustrated U-shaped sealing lips 21, 22, a one-piece sealing lip of elastically deformable material having a C shape, for example, can be provided, which can be braced, if necessary, by support material. The displaceable slide 14 can be moved, by means of a nonillustrated spindle operated by hand or by a mechanical drive mechanism, in a direction parallel to the axis of the crystalline rod 6.

Advantageously, the foregoing described and illustrated devices are applicable also to the entrance of the drive shafts 2, 3 (FIG. 1) for the rod holders 4, through the horizontal zone-melting chamber walls 18, 19, if the rod holders 4, 5 are to be laterally displaceable in a direction perpendicularly to the rod axis. An embodiment which permits lateral displacement of the lower drive shaft 2 at the lower horizontal zonemelting chamber wall 19 is shown in FIG. 5 in a sectional view. Between the lower zone-melting chamber wall 19 and a counterpressure plate 33, a slide 14 is movably mounted between ball-bearing elements 34. The sealing strip 20 again consists of U-shaped sealing lips 21, 22, which form a channel for a pressure medium 24 that is supplied, for example, through a hose 35. Openings 36 and 37 in the slide 14 limit the lateral displacement of the drive shaft 2.

lclaim:

1. Device for crucible-free zone melting a crystalline rod comprising a zone-melting chamber having a sidewall formed with a substantially vertical slot, heating means extending through said slot into said chamber and energizable for forming a melting zone in a substantially vertically supported crystalline rod mounted in said chamber, slide means located adjacent said sidewall and covering said substantially vertical slot, said slide means carrying said heating means and being slidable together with said heating means relative to the rod in the direction of the rod axis whereby the melting zone is passed through the rod, and an elastically deformable sealing strip securely mounted against displacement thereof between said slide means and said sidewall of said zone-melting chamber and completely surrounding said slot whereby said slot is gastightly sealed, said sealing strip being formed of at least one-sealing lip having a position determined by a bracing member therefor, and a pressurized fluid medium in engagement with said sealing lip for pressing it against a sliding surface of said slide means.

2. Device according to claim 1 wherein said sealing strip is formed of a plurality of sealing lips, said lips being curved toward one another and having a position determined by a bracing member in engagement therewith, and said pressurized medium being in engagement with said plurality of sealing lips for pressing them against a sliding surface of said slide means.

3. Device according to claim 1 including relatively easily moving guide elements mounted between said sidewall of said zone-melting chamber and said slide means. 

2. Device according to claim 1 wherein said sealing strip is formed of a plurality of sealing lips, said lips being curved toward one another and having a position determined by a bracing member in engagement therewith, and said pressurized medium being in engagement with said plurality of sealing lips for pressing them against a sliding surface of said slide means.
 3. Device according to claim 1 including relatively easily moving guide elements mounted between said sidewall of said zone-melting chamber and said slide means. 